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Flow field, heat and mass transfer in a jet impingement ovens: Numerical and experimental studies |
M. V. KARWE, N. Nitin, and D. Kocer. Dept. of Food Science, Rutgers, The State Univ. of New Jersey, 65 Dudley Rd., New Brunswick, NJ 08901-8520 Jet impingement technology has been used in food processing to make variety of products such as cookies, pizza, breakfast cereals and tortilla chips. The main advantages of high speed jet impingement are substantially higher rates of heat transfer, quick development of crust and more retention of moisture. It has been reported recently that this technology offers a way to retain more omega-3 fatty acids in a food product. Information on detailed transport phenomena in a jet impingement oven used for food processing is scarce and is needed for process evaluation and design. Numerical simulation of flow and temperature fields in a jet impingement oven was carried out using Fluent software. Measurement of fluid flow and heat transfer coefficient was carried out in different types of jet impingement ovens. Flow field in an Enersyst jet impingement oven was measured using laser Doppler velocimetry for a single jet and multiple jets. Average heat transfer coefficients for cookie and hot dog type objects were measured in a Wolverine Jet Zone dryer. Local surface heat flux was measured using a thin and small heat flux gages. Results indicated that flow field in the oven cavity was strongly influenced by the nozzle design. Small imperfections in the nozzle lip altered the flow field substantially. In multiple jet flow, areas of flow reversal between the jets were clearly seen. The average surface heat transfer coefficient was dependent upon object size, shape and spacing between adjacent objects. The Nusselt number (dimensionless heat transfer coefficient) showed power-law variation with Reynolds number (maximum jet velocity). The maximum value of heat transfer coefficient, at the stagnation point right under the jet, was about 20-30% higher than average heat transfer coefficient. Numerical predictions for flow field and heat transfer coefficient agreed well with the experimental results.
Session 33, Food processing with air impingement systems: Innovations and opportunities
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